Apparatus and method for manufacturing a socket end of a pipe part provided with a sealing ring

ABSTRACT

Apparatus for manufacturing a socket end ( 12 ) which is provided with a sealing ring ( 9 ). The apparatus comprises an outer mould ( 1 ) for forming the outer contour of the sealing ring ( 9 ) and for forming the outer side of the socket end ( 12 ), and a core for forming the inner side of the socket end ( 12 ) and the sealing ring ( 9 ). The core comprises a first core part ( 7   a ), a sleeve-like core part ( 7 ) which can be displaced on the first core part ( 7   a ), for forming a front for the sealing ring ( 9 ), a core part ( 8 ) which adjoins the first core part ( 7   a ) and can be contracted in the radial direction, for forming the inner contour of the sealing ring ( 9 ), and a second core part ( 6 ), which adjoins the contractable core part ( 8 ), for forming the inner side of the pipe part. The contractable core part ( 8 ) has a radially innermost position with an external diameter which is smaller than the internal diameter of the sleeve -like core part ( 7 ).

The invention relates to an apparatus for manufacturing a socket end ofa pipe part, which socket end is provided, on the inner side, with asealing ring which is fixedly connected thereto, the socket end beingmanufactured from a relatively rigid thermoplastic material and thesealing ring being manufactured from a thermoplastic elastomer which iscompatible therewith, and the socket end comprising a first cylindricalpart of a defined internal diameter, a groove part which axially adjoinsthe first cylindrical part on the outer side and has a larger internaldiameter than that of the first cylindrical part, in which groove partthe sealing ring is arranged, and an edge part which adjoins the groovepart and has a smaller internal diameter than that of the groove part,which apparatus comprises an outer mould for forming the outer contourof the sealing ring and for forming the outer side of the socket end,and a core for forming the inner side of the socket end and the sealingring.

The invention also relates to a method for manufacturing a socket end ofa pipe part, in which first of all the sealing ring is formed in a firstmould cavity, and then the socket end is formed in a second mould cavitywhich adjoins the sealing ring which has already been formed.

An apparatus and method of this type are known from U.S. Pat. No.4,173,362. In this known apparatus and method, the core, after thesocket end has been formed at the location of the sealing ring, isdivided into an axially outermost core part and an axially innermostcore part. During demoulding of the socket end, first of all the outermould is opened, and then the axially outermost core part is pulled outof the socket end. Then, the axially innermost core part is pulled outof the socket end over the sealing ring.

The known apparatus and method have the drawback that, when the axiallyinnermost core part is being pulled out of the socket end, there is arisk of the sealing ring being damaged.

It is an object of the invention to provide an apparatus and a methodfor forming a socket end of a pipe part, in which the risk of damage tothe sealing ring formed in the socket end is minimized.

SUMMARY OF THE INVENTION

Use of the apparatus and method according to the invention prevent thesealing ring from being damaged while the core is being pulled out ofthe socket end. This is because the core has a smooth surface as itslides along the sealing ring.

Advantageously, the outer mould is opened during demoulding before thesleeve-like core part is moved towards the axially innermost position,so that there is no wear to the surfaces of the core and the outer mouldwhich move along one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference tothe drawing, in which:

FIG. 1 shows a longitudinal section through an apparatus according tothe invention while the sealing ring is being formed,

FIG. 2 shows a longitudinal section through the apparatus shown in FIG.1 with an open outer mould,

FIG. 3 shows a cross section through the apparatus in a position whichcorresponds to that shown in FIG. 2,

FIG. 4 shows a longitudinal section through the apparatus shown in FIG.1 while a socket end is being formed,

FIG. 4 a shows a longitudinal section through a part of a socket endaccording to the invention,

FIG. 4 b shows a detailed view of a longitudinal section through a firstlip of the sealing ring of the socket end shown in FIG. 4 a,

FIGS. 5-7 show the successive steps involved in demoulding the socketend using the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an apparatus comprising an outer mould 1 and a core 2. Theouter mould 1 comprises a fixed mould half 3 and a movable mould half 4.The movable mould half 4 has a number of displaceable mould parts 5. InFIG. 3, the double arrow 10 indicates how the movable mould half 4 canmove with respect to the fixed mould half 3. The displaceable mouldparts 5 can be displaced with respect to the movable mould half 4. Thedirection of displacement of the displaceable mould parts is indicatedby the double arrows 11. In the preferred embodiment shown here, themovable mould half 4 and the displaceable mould parts 5 are coupled viaa slide mechanism 30 in such a manner that, when the outer mould 1 isclosed and is being opened, i.e. the movable mould half 4 is being movedaway from the fixed mould half 3, the displaceable mould parts 5 slideoutwards away from the core 2, and when the outer mould 1 is beingclosed, i.e. the movable mould half 4 is being moved towards the fixedmould half 3, the displaceable mould parts 5 slide inwards towards thecore 2. In FIG. 3, for the purpose of illustration, the slid-inwardposition of one of the displaceable mould parts 5 is illustrated by adashed line and is denoted by 5 a.

In an alternative embodiment, the coupling of the movement of themovable mould half 4 and the displacement of the displaceable mouldparts 5 may be absent, so that displacement of the displaceable mouldparts 5 can take place independently of the movement of the movablemould half 4.

The core 2 comprises a first core part 7 a, a sleeve-like core part 7which can be displaced axially on the first core part 7 a, a radiallycontractible core part 8 which axially adjoins the first core part, anda second core part 6 which adjoins the contractible core part 6 in theaxial direction.

In the position illustrated in FIG. 1, the outer mould 1 is closed. Afirst mould cavity is delimited by the fixed mould half 3, thedisplaceable mould parts 5, the sleeve-like core part 7 and the radiallycontractible core part 8. This first mould cavity is filled with athermoplastic elastomer in order to form a sealing ring 9, the outercontour of the sealing ring being shaped by a mould cavity 13 in theouter mould 1.

When the sealing ring 9 is dimensionally stable, the outer mould 1 isopened, as shown in FIG. 2 and FIG. 3. This creates space for the core 2and the sealing ring 9 formed thereon, in order to allow axialdisplacement with respect to the outer mould 1. The core 2 with thesealing ring 9 is then displaced axially towards a position which liesfurther inwards in the axial direction, in which position the sealingring 9 is located at the level of a mould cavity 27 arranged in theouter mould 1. Then, the outer mould 1 is closed, so that a second mouldcavity, which adjoins the sealing ring 9, is formed. FIG. 4 shows thatthe second mould cavity is filled by injection-moulding a relativelyrigid plastic material which is compatible with the material of thesealing ring. This rigid plastic material may, for example, bepolypropylene. In this way, a socket end 12 of a pipe part is formed.

The socket end 12 has a first cylindrical part 15 of a defined diameter.In the vicinity of the free end of the socket end 12, a groove part 16adjoins the first cylindrical part 15. The internal diameter of thegroove part 16 is greater than that of the first cylindrical part 15.From the groove part 16, an adjoining cylindrical edge part 17 extendstowards the free end. The edge part 17 has a smaller diameter than thegroove part 16.

The sealing ring 9 is accommodated in the groove part 16. The sealingring 9 comprises a first lip 18, which extends radially inwards and islocated in the vicinity of the transition between the groove part 16 andthe edge part 17. The first lip 18 has a base section 19, which extendsaxially from the first lip 18 towards the edge part 17 in the groovepart 16. The presence of the base section 19 has the advantage that,when the first lip 18 is bent radially outwards, for example whenanother pipe part is being fitted into the socket end 12, the connectionbetween the sealing ring 9 and the socket end 12 at the location of thetransition 19 a between the edge part 17 and the sealing ring 9 does nottear off. The transition 19 a is preferably smooth, so that when anotherpipe part is being inserted into the socket end 12, this pipe partcannot get stuck behind an uneven part of the transition 19 a and tearthe sealing ring 9 off the socket end 12. The transition between thefirst lip 18 and the base section 19 preferably has a certain radius.This rounding of the transition is used to prevent stress peaks in saidtransition when the first lip 18 is being bent radially outwards. At thetransition between the groove part 16 and the first cylindrical part 15of the socket end 12, the sealing ring 9 comprises a second lip 20 whichextends axially towards the first lip 18. When the socket end 12 isbeing formed in the second mould cavity, hot plastic material isintroduced, which plastic material is fixedly joined to the sealing ring9. The second lip 20 has the advantage that the inner side of thesealing ring 9 remains securely fixed to the contractible core part, sothat the hot plastic material cannot reach and affect the inner side ofthe sealing ring 9. An annular wall 21 extends along the internaldiameter of the groove part 16, between the second lip 20 and the firstlip 18. The first lip 18, the second lip 20 and the annular wall 21delimit a cavity 22, which is formed by the radially contractible corepart 8 (cf. FIG. 1). The cavity 22 lies inside the groove part 16 of thesocket end 12. The depth of the cavity 22 is greater than the thicknessof the first lip 18, so that when another pipe part is being insertedinto the socket end 12 the first lip 18 fits into the cavity 22. Theaxial length of the cavity 22 is greater than the length of the firstlip 18 and the second lip 20 together, so that when another pipe part isbeing inserted into the socket end 12 the first lip 18 and the secondlip 20 do not come into contact with and get in the way of one another.

That side of the first lip 18 which faces towards the edge part 17 isfree from radially extending unevenness, so that a good seal is obtainedand, during insertion of another pipe part into the socket end 12, it isimpossible for there to be any leakage along the first lip 18 of sealingring 9 and the inserted pipe part.

That side of the first lip 18 which faces towards the edge part 17 isprovided with continuous, encircling thickened portions 40, as shown inFIG. 4 a. Each thickened portion 40 has a radially outermost side 40 aand a radially innermost side 40 b, as shown in FIG. 4 b, each thickenedportion 40 gradually increasing on the radially outermost side 40 a anddecreasing greatly on the radially innermost side 40 b. On account oftheir shape, the thickened portions form a labyrinth seal, leading toimproved sealing.

In the text which follows, the demoulding of the socket end 12 will beexplained with reference to FIGS. 5-7. When the socket end 12 issufficiently dimensionally stable, the radially contractible core part 8can be contracted, as shown in FIG. 5.

The external diameter of the contractible core part 8 is smaller, in thecontracted position, than the internal diameter of the sleeve-like corepart 7.

Then, the outer mould 1 is opened, after which the sleeve-like core part7 is displaced axially inwards, towards the second core part 6, withrespect to the first core part 7 a. Before this displacement of thesleeve-like core part 7, the outer mould 1 is opened, in order toprevent wear to surfaces of the outer mould 1 and the core 2 which slidealong one another.

The end side 25 of the sleeve-like core part 7 is shaped in such amanner that it is complementary to an edge section 26 of the second corepart 6. This allows accurately fitting connection of he two core parts 6and 7. The sleeve-like core part 7 is slid over the radiallycontractible core part 8, and the end side 25 of the sleeve-like corepart 7 is placed against the edge section 26 of the second core part 6,as shown in FIG. 6. The external diameter of the sleeve-like core part 7corresponds to that of the second core part 6. When the sleeve-like corepart 7 and the second core part 6 adjoin one another, the core 2 has asmooth outer surface.

When the sleeve-like core part 7 is being displaced axially inwards, thefirst lip 18 of the sealing ring 9 is pressed radially outwards by thesleeve-like core part 7. The first lip 18 is pressed into the cavity 22of the sealing ring 9. Since the cavity 22 has a depth which is greaterthan the thickness of the first lip 18, the first lip 18 fits completelyinto the cavity 22, which facilitates the step of pressing the lip 18outwards. The rounding of the transition between the first lip 18 andthe base section 19 has the advantage that, during the deformation ofthe first lip 18, the material of the sealing ring is prevented fromtearing in the transition region. It is preferable for the free end ofthe second lip 20 to be directed slightly radially outwards in thecavity 22. This prevents this second lip 20, while the sleeve-like corepart 7 is sliding axially inwards, from being carried along by this corepart so that it is deformed and passes between the sleeve-like core part7 and the second core part 6, which can cause damage.

Finally, the core 2 is pulled axially out of the socket end 12 as asingle unit, as shown in FIG. 7. Since the outer surface of the mutuallyadjoining second core part 6 and the sleeve-like core part 7 is a smoothsurface, the core will slide along the sealing ring 9 with littleresistance, preventing damage to the sealing ring 9.

1. Apparatus for manufacturing a socket end of a pipe part, which socketend is provided, on the inner side, with a sealing ring which is fixedlyconnected thereto, the socket end being manufactured from a relativelyrigid thermoplastic material and the sealing ring being manufacturedfrom a thermoplastic elastomer which is compatible therewith, and thesocket end comprising a first cylindrical part of a defined internaldiameter, a groove part which axially adjoins the first cylindrical parton the outer side and has a larger internal diameter than that of thefirst cylindrical part, in which groove part the sealing ring isarranged, and an edge part which adjoins the groove part and has asmaller internal diameter than that of the groove part, which apparatuscomprises: an outer mould for forming the outer contour of the sealingring and for forming the outer side of the socket end, and a core forforming the inner side of the socket end and the sealing ring,characterized in that the core comprises a first core part, asleeve-like core part, which can be displaced on the first core part inthe axial direction between an outermost position and an innermostposition, for forming a front for the sealing ring and the inner side ofthe edge part, a contractible core part, which adjoins the first corepart in the axial direction and can be moved in the radial directionbetween an outermost position and an innermost position, for forming theinner contour of the sealing ring, and a second core part, which adjoinsthe contractible core part in the axial direction, for forming the innerside of the pipe part, the radially contractible core part, in theradially innermost position, having an external diameter-which issmaller than the internal diameter of the sleeve-like core part. 2.Apparatus according to claim 1, in which the sleeve-like core part, inthe axially outermost position, adjoins, by means of its end side, thecontractible core part, which is in the radially outermost position,and, in the axially innermost position, adjoins, by means of an endside, the second core part in a fitting manner, in which arrangement, inthe situation in which the sleeve-like core part is in the axiallyoutermost position and the contractible core part is in the radiallyoutermost position, the sleeve-like core part adjoins, by means of itsend side, the contractible core part and, in the situation in which thesleeve-like core part is in the axially innermost position and thecontractible core part is in the radially innermost position, thesleeve-like core part, by means of its end side, adjoins the second corepart, the contractible core part being situated inside the sleeve-likecore part.
 3. Apparatus according to claim 1, in which the sleevelikecore part, in the axially innermost position, adjoins the second corepart in a fitting manner, such that the core has a smooth outer surface.4. Apparatus according to claim 1, in which the outer mould has a fixedmould half and a movable mould half, the movable mould half beingmovable substantially perpendicular to the centre axis of a mould cavitywhich is enclosed by the outer mould in the closed position. 5.Apparatus according to claim 4, in which the movable mould half has anumber of displaceable mould parts which can be displaced transverselyto the direction of movement of the movable mould half and substantiallyperpendicular to the centre axis of the mould cavity.
 6. Apparatusaccording to claim 5, in which the movable mould half and thedisplaceable parts thereof are mechanically coupled in such a mannerthat the movement of the mould half simultaneously causes displacementof the displaceable mould parts.
 7. Apparatus according to claim 4, inwhich the core is mechanically connected to the movable mould half insuch a manner that the core substantially follows the movement of themovable mould half when the mould is being opened.
 8. Method formanufacturing a socket end of a pipe part, which socket end is provided,on the inner side, with a sealing ring which is fixedly connectedthereto, the socket end being manufactured from a relatively rigidthermoplastic material and the sealing ring being manufactured from athermoplastic elastomer, and the socket end comprising a firstcylindrical part of a defined internal diameter, a groove part whichaxially adjoins the first cylindrical part on the outer side and has alarger internal diameter than that of the first cylindrical part, inwhich groove part the sealing ring is arranged, and an edge part, whichadjoins the groove part and has a smaller internal diameter than that ofthe groove part, use being made of the apparatus according to one of thepreceding claims, which method comprises the following steps: mouldingthe sealing ring in a first mould cavity which is delimited by the coreand the outer mould, the sleeve-like core part being located in theaxially outermost position and the contractible core part being locatedin the radially outermost position, opening the outer mould, displacingthe outer mould and the core with the sealing ring thereon in the axialdirection with respect to one another, and closing the outer mouldagain, during which process a second mould cavity is formed, whichadjoins the sealing ring which has already been formed, forming thesocket end in the second mould cavity, during which process the socketend and the sealing ring are fixedly connected to one another,demoulding the socket end, during which process the contractible corepart is pulled radially inwards towards the radially innermost position,the sleeve-like core part is pushed over the retracted contractible corepart into the axially innermost position, in which it adjoins the secondcore part in a fitting manner and then the core as a unit is pulled outof the socket end in the axial direction.
 9. Method according to claim8, in which the outer mould, during the demoulding, is opened before thesleeve-like core part is moved towards the axially innermost position.